Television apparatus



April 19, 19

o. SCHRIEVER mmess TELEVISION APPARATUS Filed Dec. 1, 1953 ANTENNACURRENT INVENTOR 077'0 Patented Apr. 19, 1938 UNiTED STATES PATENE@FEFEQE TELEVESEON APPARATUS tion of Germany Application December 1,1933, Serial No. 700,457 in Germany December 2, 1932 4 Claims.

This invention relates to a method of and means for telesynchronizationof television apparatus.

For synchronizing television receivers from the transmitter there havein the main been proposed two ways and means, to wit, to transmitsynchronizing impulses diiiering from the picture impulses or signalseither by large amplitude or a distinct frequency character. But neitherprocedure has so far resulted in any really practical solution to thesynchronizing problem, though the latter, as is well known, is of utmostimportance in connection with television. arts. The reasons are these:The method first mentioned is predicated upon amplitude selection at thereceiving end, and the same operates with fairly adequate reliablenessif the amplitude of the synchronizing impulses are chosen at least twiceas strong as that of the picture signals proper. But this means thatonly one-fourth of the trans mitter power becomes available for thepicture, impulses, which, in turn, means a serious limitation in therange of the transmitter. The second method requires frequency selectormeans at the a receiving end, and this would appear practicable onlywith a considerable expenditure for circuit elements for that end.

The present invention has as one of its main objects that of providingways and means adapted to remedy this situation. The invention will beexplained in the following description taken together with the drawingin which Fig. 1 shows graphically the relation. between antenna currentand time for use in explaining the operation of the invention;

Fig. 2 shows diagrammatically a modulation circuit embodying theinvention, and

Fig. 3 shows schematically a portion of a receiver adapted to work inaccordance with the invention. It consists inthat the transmittercurrent of relatively low static value, Ir (see Fig. l) which, forinstance, may be assumed to be ,th the maximum amplitude Im(corresponding to the transmitter energy above line) is modulated orshifted by the picture signals (time interval T1) in proportion to thebrightness values in upward direction, i. e., towards larger currents,while by the synchronizing signals (time-interval T2) it is caused todisappear entirely, and that the synchronizing device locally mounted inthe receiver station is of such property that it will only respond incase of zero keying (modulation) at the sending end.

A method of this nature offers the advantage that for synchronizingpractically no additional (Cl. l78--6) transmitter energy needs to beexpended seeing that the maintenance of a slight residual current of anorder of magnitude as hereinbefore stated, as is well known, is anywayuseful for the insurance of high picture quality insofar as in thatmanner the non-linear lower end of the can tenna current characteristicin the modulation oi the picture signals is avoided. Another meritresides in the great simplicity of the receiving arrangements.

Fig. 2 shows fundamentally an exemplified embodiment of the meansrequired at the sending end with a View to practice the basic idea ofthe present invention. Suppose that AB is the line or plane of motion ofthe scanning spot, and CB the dead or blind picture angle assumed to beavailable for synchronization. Let D be, for instance, a film conveyedat right angles to the plane laid through the drawing and which is to betransmitted. through the film is supposed to be directed towards aphotoelectric cell E, while for the duration of the synchronizinginterval, the spot, being of constant intensity, is directed towards thephotocell F. Both of these photoelectric cells are fed by way oi thetransformer G, or else by way of two distinct transformers, withalternating potential of the same frequency. H and I are theneutrodyning condensers provided to compensate the capacitive cellcurrent, K and L two parallel resistances serving as phase shifters. Mand N are two amplifier tubes, which at the anode end, work upon one andthe same resistance 0. Neutralization of the two photoelectric cells,according to this invention, is effected in the presence of contraryilluminations, to be more precise, so that one thereof (E) is neutral inthe absence of light, and the other one (F) in the presence of light.The result is that during the scanning of the picture, there willpersist across the terminals PQ a constant, non-modulated residualvoltage of the carrier wave, which will disappear only during theinstants when the cell F is irradiated, that is, during the blindpicture angle at the end of each line. In other words, the times withabsence of current govern the change in line.

In a very similar way, one or more non-modulated lines between pairs ofpictures may be utilized for the change in picture in that the lightoriginating therefrom is also directed towards photocell F by theintermediary of suitable optical means.

The desired relationship between residual voltage and signal potentialis regulable by the aid of the slider on contact 0. Associated with theThe light permitted to pass points PQ in well known manner is anamplifier for the carrier wave whence the signals are fed to themodulator of the transmitter.

So far as the operation of the idea underlying the invention isconcerned, it is immaterial Whether the carrier frequency is included inthe transmission or whether prior to transmission demodulation iseffected with suppression of the auxiliary carried. Neither is itabsolutely necessary to combine the two photocell circuits withfollowing amplification into one unit as assumed in Fig. 2, for as amatter of fact, both cells may be provided with separate amplifyingmeans. But it is preferable in this connection to derive the carrierfrequency from one and the same generator. Neutralization, finally, neednot be effected directly at the photoelectric cells, indeed, this may beaccomplished at some other point in the course of amplification bycircuit schemes known in the earlier art.

The ways and means to be adopted at the receiving end with a view topracticing the basic idea of the invention shall be explained in moredetail at least in principle by reference to Fig. 3. The radio receiver5, say a transposition type of receiver shall be assumed to comprise anaudio frequency output transformer (or some other coupling means) withtwo secondary windings 3 and 4. posed to be employed, as known in theprior art, for the brightness (light) control of the receivingapparatus, which, as to the rest, may be of any suitable pattern,whereas the second winding 4- shall serve for synchronization. With thisend in view, a rectifier 5 is provided in series with a resistance 6which is so connected as to act at the same time as the grid leak oftube The transformer windings and other circuit elements are. so chosenthat, with proper and thorough modulation of the receiver light thedirect current component arising at 6 will also suffice for blocking thetube 1 as long as the transmission current is greater than, or equal to,the static value Ir (Fig. 1, time intervals T1) but if, on the contrary,the transmission current drops to zero (intervals T2), tube 1 because ofnot being blocked assumes a state where current is transmitted. In casethe Braun tube serves as a reproducing device, tube 7, for instance, inthe form of a thyratron may be connected directly as a discharge tubefor a pair of deflector plates. If the receiver comprises a localsynchronizing source (relaxation wave or other generator), then thecurrent impulses furnished from 1 may be utilized for synchronizing thelatter (for instance, by what is known as entrainment or coherenceaction).

The times T2 (Fig. l) are utilized in a way as described forline-change. For the. change of pictures, say, between two consecutivepictures, there will be no objection in sacrificing the time of severallines so that the corresponding times where current is absent will, asto order of magnitude, be 100 times as long as the periods when alinechange happens. For the automatic regulation of picture change thereshall be supposed to be provided a similar circuit l, 5, 6, I) as forthe change of lines, except that in parallel relation to the resistance6 a condenser 3 shall be assumed to be connected being of such a sizethat the linechange impulses will practically produce no alteration inthe direct current voltage drop at 6 and are thus precluded from tube 1,so that only the One of these windings, say 3, shall besuppicture-change impulses will become operative in this circuit. On theother hand, safeguarding of the line-change device from thepicture-change impulses is not required inasmuch as every picture-changecoincides with a line-change.

Particular attention must be drawn to the great simplicity oftele-synchronization of Braun tubes by the ways and means heredisclosed, and also to the great efficiency and economy attained in thebuilding of receiver equipment.

The invention is suited equally for radio as well as for wiretransmission.

I claim:

1. A system for synchronizing television apparatus, comprising lightresponsive means to produce signals representing sequentially occurringlight values on elemental areas of an elemental strip of a subject,light responsive means to produce signals representing a completion of aseries of signal represented light values, an amplifier system foramplifying the produced signals, means to control the first mentionedsignal producing means to provide a predetermined minimum outputdifferent from zero from the amplifier in the absence of light in saidfirst signal producing means, and means to provide substantially zerooutput from the amplifier when light is present in said second signalproducing means.

2. A system for synchronizing television apparatus comprising means toreceive repeating series of signals each separated by an absence ofsignals to represent synchronizing periods, comprising means to receiveand amplify the signals, means to produce from the signalsproportionally varied electro-optical effects, a rectifying deviceconnected with the receiver amplifier means, an electronic tubeconnected with the output of the rectifier, and means for controllingthe electronic tube by the rectified signals to bias the tube to zerooutput during periods of signal reception and to remove the bias toprovide maximum output only during predetermined periods ofinterruption.

3. A system for synchronizing television apparatus, comprising lightresponsive means to produce signals representing sequentially occurringlight values of elemental areas of an elemental strip of a subject,means to modulate carrier wave energy in accordance with said producedsignals, means for amplifying the modulated carrier wave energy, a loadcircuit for said amplifying means, means to provide a predeterminedminimum of unmodulated carrier wave energy different from zero in theload circuit in the absence of light in the first named means, and meansfor reducing the minimum carrier wave energy to zero only atpredetermined time intervals.

4. A system for synchronizing television apparatus, comprising lightresponsive means to produce signals representing sequentially occurringlight values of elemental areas of an elemental strip of a subject,means to modulate carrier wave energy in accordance with said producedsignals, means for amplifying the modulated carrier wave energy, a loadcircuit for said amplifying means, means to provide a predeterminedminimum of unmodulated carrier wave energy different from zero in theload circuit in the absence of light in the first named means, and meansfor reducing the minimum carrier Wave energy to zero only at the end ofscanning each elemental strip.

OTTO SCI-IRIEVER.

